Transistors, and in particular organic field effect transistors (OFETs), are used e.g. as components for printed electronic devices such as organic light emitting display, e-paper, liquid crystal display and radiofrequency identification tags. An OFET comprises a semiconducting layer comprising an organic semiconducting material, a dielectric layer comprising a dielectric material, a gate electrode and source/drain electrodes.
Especially desirable are OFETs wherein the dielectric material can be applied by solution processing techniques. Solution processing techniques are convenient from the point of processability, and can also be applied to plastic substrates. Thus, organic dielectric materials, which are compatible with solution processing techniques, such as spin coating, allow the production of low cost organic field effect transistors on flexible substrates.
EP 1 1 459 392 A discloses a process of manufacturing an organic field effect device comprising depositing an organic semiconductor layer from a solution, followed by depositing from a solution a layer of low permittivity insulating (i.e. dielectric) material forming at least a part of a gate insulator. The organic field effect device may further comprise a high permittivity insulating layer deposited on the other side of the low permittivity insulating layer. According to EP 1 1 459 392 A, the organic semiconductor layer may be a homopolymer or copolymer comprising the typical structural units arylamine, fluorene and thiophene. The semiconductor layer is coated on a substrate from an aromatic or chloroaromatic solvent such as toluene. The low permittivity insulating material of EP-A1 1 459 392 which may be based on polystyrene is preferably a fluoropolymer which is deposited on the organic semiconductor layer from a fluorosolvent which does not dissolve the semiconductors typically used in OFETs. The high permittivity insulating material may be also based on a fluoropolymer and is preferably deposited from a fluorosolvent.
WO 2012/059386 discloses a process for the preparation of a transistor on a substrate, the transistor comprising an insulating layer comprising a polyimide, wherein the polyimide is obtained by forming on the substrate a layer comprising a photocurable polyimide and further polymerizing the polyimide by irradiating with light of a wavelength of at most 360 nm. The photocurable polyimide is obtainable by reacting a dianhydride carrying at least one photosensitive group with a diamine carrying at least one crosslinkable group. The dianhydride carrying at least one photosensitive group may be a benzophenone derivative carrying two functionalities —C(O)—O—C(O)—. The diamine carrying at least one crosslinkable group may be an organic compound carrying two amino functionalities and at least one aromatic ring having attached thereto at least a CH2 or a CH3 group or at least on carbon-carbon double bond. For subsequent application to a substrate, a semiconductor layer is applied from an organic solvent such as toluene, and the insulating layer is applied from an organic solvent such as N-methyl-pyrrolidone, cyclopentanone, methyl ethyl ketone or ethyl acetate.